Conventional projection display apparatuses represent images by conducting to a DMD (digital micro-mirror device)™ or an optical valve, an optical beam emitted from an optical source via optical elements such as lenses and mirrors and then projecting an output imaging beam on a screen. In such conventional display apparatuses, the above-described optical element provides an optical path difference to the optical beam, which leads to mutual interference between optical beams, thereby causing speckle (or speckle noise) to occur. Thus, in order to reduce occurrence of the speckle, an optical component causing a slight optical path difference is arranged to be placed in an optical path. Furthermore, in order to effectively reduce the occurrence of the speckle, a drive unit causes rotation of optical components placed, as is disclosed in Japanese Unexamined Patent Publication No. 2002-90881, thereby generating various speckle noise patterns and then reducing the speckle noise by visually averaging the patterns.
However, as shown in Japanese Unexamined Patent Publication No. 2002-90881, a problem is that when a flaw exists in or dust on the optical component for an apparatus having an optical component causing an optical path difference simply disposed in an optical path, the image of the flaw or dust is projected on the screen, thus resulting in an image defect on the screen, which leads to a reduction in image quality.